DESCRIPTION (Applicant's Abstract): Memory is a critical component of human cognition, with major implications for everyday life and mental health. However, memory is not a unitary or monolithic entity, but instead consists of a variety of dissociable processes and systems. The proposed experiments use positron emission tomography in an attempt to map the component process and systems involved in explicit memory (conscious recollection of previous experiences) and implicit memory (nonconscious effects of past experiences on subsequent behavior and performance). Within the domain of explicit memory, preliminary data suggest that the hippocampal formation is sometimes associated with the conscious recollection of recent experiences -- successful remembering of an event -- as opposed to strategic efforts to retrieve a recent event. Experiments 1-3 examine this possibility, and also explore the role of prefrontal cortex in explicit retrieval, by using experimental manipulations that provide a basis for distinguishing between, and characterizing the nature of, processes involved in successful remembering on the one hand and effortful retrieval attempts on the other. These experiments also examine the types of retrieved information that are associated with hippocampal blood flow increases, and also explore the role of medial temporal and frontal regions in illusory memories. Experiments 4-6 investigate implicit memory, focusing on the neuroanatomical correlates of visual and auditory priming. These experiments test specific hypotheses about the neural basis of priming that are generated by a theoretical framework developed by the principal investigator. Previous research has revealed that preserved priming and other implicit memory abilities in amnesic patients can provide a basis for developing effective rehabilitation strategies that have significant effects on patients' everyday lives. The proposed studies will provide new information about the neuroanatomical correlates of implicit memory and thereby contribute to the further development of rehabilitation efforts.